Updated with Nurburgring video.

The long awaited four-door Aston Martin Rapide has been spotted, almost completely undisguised, doing laps of the Nurburgring. This latest video of the prototype includes some close-up shots of the car as it enters and exits a trackside testing facility as well as some high speed runs around the popular circuit. We also for the first time can hear the rumble of the V12 mill at full tilt as the svelte sedan barrels past the camera’s microphone.

Previous prototypes were last spotted on the frozen lakes of Sweden for winter testing, and somewhere in between its journey from Sweden to Germany the Rapide was given a full-length glass roof. While the rear lights in the spy shots are similar to the plain red ones found on the DB9, it is uncertain whether the production version will share the same clear taillights of the original concept version from 2006’s Detroit Auto Show.

Other than this, the testing model remains faithful to the stunning concept and it looks like it’s shaping up to be one of the best looking four-doors on the planet. Porsche’s upcoming Panamera and the Mercedes CLS will have a tough time competing with the new Aston, which is expected to develop upwards of 500hp in some guises. A less powerful V8 model is expected to debut after the launch of the introductory V12 range-topper.

Unfortunately for purists, the Rapide will not be built at Aston’s traditional Gaydon plant in England - production of the four-door has been contracted to Magna Steyr who will build the vehicle at its Austrian plant.

Production is expected to start in 2009 for the Rapide, giving it ample time to get into the market against the upcoming Panamera, although rivals like the CLS and Maserati Quattroporte already have a big head start over the new four-door Porsche and Aston.

Aston Martin Rapide prototype with glass roof